Control mechanism



Feb. 10, 1931. J R 1,792,241

CONTROL MECHANISM Filed July 30, 1929 WITNESS INVENTOR 6.1 I J. L. RAY.BY

ATTORNEY Patented Eel 10, 1931 UNITED- s'ra'ras PATENT OFFICE JAMES L.BAY, OF SWABTHMOBE, PENNSYLVANIA, ASBIGNOB '10. WESTINGHOUSE ELECTRIC &MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA CONTROL MECHANISM YApplication filed July 30,

My invention relates to a control mechanism for a prime mover, moreparticularly to a load-responsive control for a prime mover, and it hasfor its object to provide a mechanism of this character which willminimize the increase in speed upon a sudden removal or decrease in theload thereof.

My invention is adapted, more particularly, to a steam turbine of largecapacity driving an electric generator. While carry, ing full or a heavyload, the quantity of steam in the casing is very great and theadmission valve or valves are, fully 0 en, or

nearly so and admit large quantities o steam.

' In the event that the c1rcuit breaker for the generator opens, theentire load on the turbine generator unit is removed, and the speedthereof is increased by the large quantity of steam inthe turbine casingand by the no steam being admitted through the open ad mission valves. Ashort but appreciable eriod of time is required, after such event, forthe speed to accelerate to the point at which the governor acts to closethe admission valves, during which period of time the admission valvesremain open and admit an amount of steam, which, together with the steamin the casing at the moment of load removal, is sufficient to produce anover-speed .30 great enough to effect operation of the autostopgovernor. It is desirable to avoid operation of the auto-stop governor,as this requires resetting thereof, and also manual operation of themassive throttle valve before the unit can be restarted.

The steam in the casing at the moment of load drop may be sufiicient toincrease the speed somewhat above the normal operating speed, but it isnot enough to increase the speed sufliciently to operate the auto-stopgovernor. A control mechanism therefore, which effects closing of theadmission valve during the interval of time between the moment of loaddrop and the increase in speed to the oint where the governor will shutthe 8111111881011 valves, will avoid operation of the auto-stopgovernor.

In accordance with my invention, I provide, in addition to the usualspeed governor, a mechanism which is responsive to the 1929. Serial No.382,286.

load on the prime mover, and which effects immediate closing of theadmission valve, independently of the governor action, upon decreasein'load by a predetermined amount below the load for which the overningmechanism is positioned to admit motive fluid. In other words, theminimum load below which the control mechanism efl'ccts closing of theadmission valve is varied by the position of a part of the governormechanism, as by the adjustment of the speed changer.

The above and other objects are effected by my invention, as will beapparent from the following description and claims taken in connectionwith the accompanying drawin s, forming a part of this application, inWhic The figure is a diagrammatic view showing my novel controlmechanism applied to a prime mover driving an electric generator.

Referring to the drawing more in detail, I show a turbine-generator unitincluding an elastic fluid turbine 10 driving a synchronous alternatingcurrent generator 11. The generator 11 delivers electric current to apower line 12 through leads 13, in which is disposed a circuit breaker14.

The turbine 10 is supplied with motive fluid from a conduit. 15, througha valve 16 which controlsthe admission thereof to the turbine. The valve16 is controlled by a speed responsive governor 17 through a fluidpressure relay mechanism- 18. The relay mechanism 18 includes a motordevice 19 connected to the valve 16 by a rod 16 and controlled by avalve 20. The latter is operated by a lever 22, which is connected,intermediate its ends, to the pilot valve, as indicated at 23', and atone end to the rod 16. It also includes an auxiliary pilot valve 21adapted to control the motor device 19'to elfect complete closin of thevalve '16 regardless of the action 0 thepilot valve 20. The relaymechanism is not shown in detail for the reason that the same is wellknown in the art, one suitable form being fully described in Patent No.1,151,522, issued August 24, 1915, to Francis Hodgkinson. For thepurpose of the present description, the lever 22 may be considered asfulcrumed at 23.

The governor 17 may be of any suitable construction and is here shown asof the flyball type. It is pivotally connected to a lever 24, fulcrumedon a stationary part at 25,

' At its other end, the lever 24 is connected to a speed changermechanism 29, the connection including a lever 31, fulcrumedintermediate its ends, as at '32, and connected to the other end of thelever 24 by means of a short link 33.

The speed changer mechanism 29 includes a spring 34 connected at itsupper end to the lever 31 and at its lower end to a spring holdingmember 35. The spring holding member 35 is attached to the upper end ofa screw threaded stem 36, whose vertical position is controlled by aworm gear 37 actuated by a speed changer motor 38.

The apparatus so far described is old and well known, and operatesbriefly as follows:

Upon a decrease in load on the generator 11 and an increase in speed,the governor 17 moves the right hand end of the lever 24 upwardlyagainst the force of the spring 34, thereby.moving the left-hand end ofthe lever 22 upwardly. The relay mechanism thereupon moves the'valve16in closing direction td decrease theadmissionof motive Upon increasein load and decrease in speed, the right-hand end of the lever 24 ismoved downwardly and the admission valve 16 ismoved in openingdirection.

To'raise the speed setting of the governor, the speed changer motor 38is operated to lower the stem 36 by means of the gear 37.

As will be a parent from'the drawing, this operation e ects, through theconnecting levers, an increased opening of the admis- S1011 valve,whereupon the speed increases until the increased force of the governoreffects an increased deflection of the spring 34. To lower the speedsetting, the speed changer motor 38 is operated to raise the stem 36.

To the above-described apparatus, I add my novel control mechanism whichactuates the auxiliary pilot valve 21 ofthe relay mechanism 18. Thiscontrol mechanism includes a circuit 39, in which is interposed asolenoid 51 for operating the auxiliary pilot'valve 21. Any suitablemeans, such as a battery 52, may be provided forsupplying electriccurrent to the circuit, and the clos ng of the circuit is controlled bya switch 41, normally biased to open position by a spring 42.

The switch 41 is adapted to be .closed by a device 43, which isresponsive to the load on the generator 11 and is adapted to close theswitch 41 upon suflicient decrease in load. The device 43 preferablyincludes a solenoid 44, which is energized in accordance with the flowof current through the leads 13 in any suitable manner, as by thecurrent transformer coil 53 arranged in circuit with the solenoid 44.Disposed within the solenoid 44 is a core 45 which is adapted to drop bygravity to close the switch 41 when the core is insuflicientlyenergized, and to be raised by the solenoid 44 to open the switch 41when the solenoid 44 is sufficiently energized.

In accordance with my invention, the auxiliary pilot valve 21 isoperated by my novel control mechanism when the load on the generator isa predetermined amount less than that for which the governor 17 ispositioned and accordingly the setting of the load-responsive device 43is controlled by some part of the governing mechanism whose positioncorresponds to the amount of motive fluid being admitted by the valve16. In the present embodiment, this is accomplished by suspending thecore 45 from the stem 36 of the speed changer mechanism through a spring47. Suitable adjusting means for varying the setting of theload-responsive devlce for a givenspeed setting of the governor ispreferably provided such as a screwthreaded connection 50 between thespring 47 and the core 45. r

The operation of the above described em bodiment is as follows: t

As is understood in the art, the speed changer is operated in accordancewith the load carried on the turbine, that is, as the load increases thespeed setting is raised in order to obtain the increased admission valveopening without a change of speed. This is more particularly true wherethe turbine drives a synchronous generator electrically connected toother generators in a system so that all the generators must run at thesame speed. Here, theload on any one generator can be changed only bychanging the speed setting. The position of the speed changer stem 36may, therefore, be taken as a function of the load on the unit.

The core 45 is biased downwardly by gravity. It is biased upwardly bythe spring 47 and further b the magnetic effect of the solenoid 44, wich varies with the load on the turbine. The adjusting means 50 is setso that when the generator 11 is carrying the load corresponding to theadjustment of the speed changer as determined by the position of thestem 36, the switch 41 is open.

When the load decreases, however, a prcdetermined amount below saidcorresponding load, the solenoid 44 permits the core to close the switch41. The circuit 39 is thus completed and the solenoid "51 operates theauxiliary valve 21. The latter controls the motor device 19 to efiiectcomplete closing of spring force for a given amount of necessary toclose t cordance with the load corresponding to that for which the speedchanger is set.- As the speed setting is raised for increased load, by.lowering the stem 36, the deflection of the spring 47 is decreased.Hence, the generator must carr a greater load to hold the core 45 aainst c osing the switch 41. Conversely, w on the s eed setting islowered for de creased 'loa by raising the stem 36, the deflection ofthe spring 36 is increased, and the low load on the generator at whichthe switch 41 closes, is decreased. As the speed setting is lowered tosome suitable light load at Which the speed governor can satisfactorilyrestrict the speed in case of load drop, the force of the s ring 47alone becomes suflicient to hold t e core 45 against closing the switch41; thus at lightloads, the control mechanism is not operative.

The amount which'the load on the generator must decrease, below the loadcorresponding tothe adjustment of the speed changer, to close the switch41, may be the same for all settings. This is done by adjusting therheostat so that the solenoid 44 effects a change in'bias equal to thechan e in load change. The amount of the necessary decrease may then bevaried by the adjustment 5(). On the other hand, the rheostat 46 may beadjusted to var ing amounts of decrease he switch 41 with varyingadjustments of the speed changer. While the unit is carrying asubstantial load, i. e. a load as great as the amount of decreasenecessary to close the switch 41, it

I the load on the enerator be removed, as by opening of the circuitbreaker 14, the admission valve 16 is promptly brought to completelyclosed position. Before the circuit breaker 14 can again be closed, thespeed of the unit must be brought exactly to synchronous speed, that is,the speed at which the alternations of the current of the generator 1.1are in synchronism with the alternations of the current in the line 12.This operation is commonlv known in the art as synchronizing, and iseffected by lowerin the s p setting to the point at which t e nocadspeed corresponds to the synchronous speed or frequency in the line 12.As above described, when the speed setting is lowered suificiently, theswitch 41 is opened independentl of the load on the generator, renoerative to derin t e governor 17 full g y uid to the control theadmission of motive turbine.

During normal operation, the load on the generator does not vary greatlyfrom that corresponding to 'the setting of the speed changer, andcontrol of the admission valve by the speed governor 17 is notinterfered .with.

It will thus be seen that I hav e provided a novel control mechanismwhich permits thespeed governor to control the admission valve at allloads during normal operation, but effects immediate closing of theadmission valve if a substantial load is removed from the generator.Thus overspeeding' in case-of load drop due to o ning of the circuitbreaker' is avoided. y avoiding overspeeding, the necessity of resettingthe automatic sto governor (not shown) ,and reopening the throttle valve(not shown) 15 eliminated, it being only necessary to change thespeed'setting to render the governor operative and to permit the unit tobe restored to the line. V

While I have shown my invention in but one form, it will be obvious tothose skilled in the art that it is not so limited, but is susceptibleof various changes and modifications, without departing from the spiritthereof,

and I desire, therefore, that only such limi-H tations shall be placedthereupon as are imposed b the prior art or asare specifically set fortin the appended clalms. I

What I claim 1s: a 1 g.

1. The combination with a prime mover having a speed governor and a.speed ,changer for the governor, of means responsive to the load on therime mover and -o rative to shut off the admission of motive flu1d tothe operative stages thereof upon decrease below a predetermmed minimumload, and means conand means controlled by the position of the,

speed changer mechanism for adjustin the first-mentioned means to varythe pre etermined minimum load.

3. The combination with a prime mover having an admission valve and anelectric generator driven thereby, of a governor mechanism for normallycontrolling the admission valve and including a speed-responsivegovernor, means efi'ectmg complete closing of the admission valve,independently of the action of the governor, upon decrease inload on thegenerator below a predetermined minimum load, and means controlledbiy'the governing mechanism for changing t e setting of thelast-mentioned means tovary said predetermined-minimum load with changesin the load to which the governing mechanismis ositioned.

4. The com ination with a prime mover and an electric generator driventhereb of a governor responsive to the speed c the prime mover fornormally oontrolling the admission of motive fluid to the prime moverand having a part whose position varies in acoordance with the admissionof motive fluid, means responsive to the electric load on the generatorfor effecting closing movement of the admission valve, independently ofthe governor action, upon decrease below a predetermined minimum' load,and means controlled by the position of said governor part for adjustinthe first-mentioned means to vary the pre etermined minimum load.

5. The combination with a prime mover having'an admission valve and anelectric generator driven thereby, of a governor responsive to the speedof the prime mover for normally controlling the admission of motivefluid thereto, and having a part whose position normally varies with theamount of motive fluid admission determined byv the governor,a relay foroperating the admission valve, said relay havin a pilot valve controlledby the governor or normally controlling the admission valve and' anauxiliary pilot valve adapted to effect closing of thet admission'valveindependently of the action of the first-mentioned ilot valve, and meansfor operating the aux iary pilot valve upon decrease in load on thegenerator by a predetermined amount below the load corresponding to theposition of said governor part.

a governing mechanism responsive to the speed of the 823119 mover. fornormall controlling the a ssion of motive fluid t ereto and having apart whose position normally varies in accordance with the admission ofmotive fluid, means responsive to the load on the prime mover for comletely shutting oil? the admission of motive uid, independently of thespeed-responsive action of the govern-' ing mechanism, upon decreasebelow a predetermined minimum load, and means controlled by the positionof said governor part for adjusting the load-responsive means to varythe predetermined minimum load.

In testimony whereof, I have hereunto subscribed my name to this 25thday of July,

'- 1 JAMES L. RAY.

6. The combination with aprime mover, of

